The present invention relates to a thrust reverser for a turbofan-type turbojet engine in which pivotable thrust reverser doors change the direction of flow of gases passing through a cold-flow air duct to provide thrust reversing forces.
Turbofan-type turbojet engines are well-known in the art and comprise an annular housing concentrically arranged around the turbojet engine housing to define a generally annular cold flow gas duct extending along the longitudinal axis of the engine. A fan, driven by the turbojet engine, is located in the upstream portion of the cold flow gas duct to force a gas, such as air, through the duct to augment the thrust of the turbojet engine.
In such turbofan-turbojet engines having a high bypass ratio, a thrust reversing device may be associated with the annular housing to redirect at least a portion of the air passing through the cold flow gas duct to provide a thrust reversing force. It is known to provide one or more pivotable thrust reversing doors in the annular housing to redirect the cold flow gas laterally outwardly through lateral openings in the housing.
A known prior art pivoting door thrust reverser, set forth in U.S. Pat. No. 5,039,171, is illustrated in FIGS. 1 and 2. As can be seen, the thrust reverser comprises thrust reverser door 7 located on a housing having an upstream portion 1 and a downstream housing portion 3. The door 7 is pivotally attached to longitudinally extending portions of the housing interconnecting the upstream portion 1 and the downstream portion 3 so as to pivot about axis 27 between a forward thrust position, illustrated in FIG. 1, and a reverse thrust position, illustrated in FIG. 2. When in the forward thrust position, an outer surface 9 of the thrust reverser door 7 lies substantially flush with the outer surfaces of the upstream portion 1 and the downstream portion 3 of the housing so as to provide an aerodynamic outer surface to the housing. In this position, an inner surface 11 of the thrust reverser door 7 forms a portion of the outer boundary of the air duct through which the gases are directed.
This known system also incorporates a thrust reverser panel 20 that is pivotally attached to the housing so as to pivot about an axis 28 between a forward thrust position, illustrated in FIG. 1, and a reverse thrust position illustrated in FIG. 2. The thrust reverser panel 20 is connected to a thrust reverser door 7 by link 22 such that both the panel and the door move simultaneously between their forward thrust positions and their reverser thrust positions.
An actuator, in this particular instance a hydraulic cylinder having an extendible and retractable piston rod, is attached to a structure 6 forming a part of the upstream portion 1 of the housing and has the piston rod pivotally connected to inner structure 12 of the thrust reverser door 7 by pivot 10. Extension of the piston rod causes the thrust reverser door 7 and the thrust reverser panel 20 to move from their forward thrust positions to their reverse thrust positions, while retraction of the piston rod causes these elements to return to their forward thrust positions. The thrust reverser door 7 may incorporate a deflector 13, also known in the art, to impart a forward direction to the gases being redirected by the thrust reverser door when in its reverse thrust position.
This known thrust reversing system improves the forward thrust performance of the turbofan engine since the inner surfaces of the thrust reverser door 7 and the thrust reverser panel 20 form a part of the outer boundary of the duct which provides smooth, aerodynamic gas flow through the duct.
While this known system has been generally successful, in special cases it has characteristics which may be undesirable. For instance, when the aerodynamic flow lines assume certain configurations, especially regarding a shallow flow, the pressure from the gasses acting on the thrust reverser panel 20 urge it toward its open or reverse thrust position. The kinematic constraints imposed upon this design locate the pivot axis 28 towards the rear or downstream portion of the thrust reverser panel 20 such that the length 1.sub.1 between the pivot axis 28 and the rearmost edge of the thrust reverser panel 20 is less than length 1.sub.2 between the axis 28 and the front, or upstream, edge of the thrust reverser panel 20. Thus, the resultant of the forces acting on the inner surface of the thrust reverser panel 20 will generate a torque in the direction of arrow P1 on the thrust reverser panel 20, which, in turn, is transmitted to the thrust reverser door 7 via the link rod 22 in the direction of arrow F1. The direction of this force F1 will generate a torque about pivot axis 27 in the direction of arrow P3 urging the thrust reverser door 7 toward its reverse thrust position. This will occur even if the pressure from the gases in the flow duct acting on the inner surface of the thrust reverser door 7 produce self-cancelling torques in the direction of arrows P3 and P2 due to the relatively equal lengths 1.sub.3 and 1.sub.4 between the downstream edge of the inner surface of the thrust reverser door 7 and the pivot axis 27, and the distance between the upstream edge of the inner surface of the thrust reverser door 7 and the pivot axis 27, respectively.
Another drawback occurs due to the kinematic geometry of this system. As best illustrated in FIG. 2, a recess or cut-out is required in the upstream edge of the thrust reverser panel 20 to provide clearance between this edge and the actuator 8. Such a recess may be relatively large, which will degrade the structural strength of the thrust reverer panel 20 while increasing the difficulty of sealing the front edge of the panel 20 when in its forward thrust position.